1. Field of the Invention
The invention relates to methods for treating condensed vapor streams containing odorous vapors. In particular, the invention relates to methods for oxidizing condensate streams in, for example, a rendering or pet food manufacturing facilities.
2. Description of Related Art
Control of odors is one of the most challenging problems faced by the animal byproduct processing industry, referred to as rendering. In most facilities animal byproduct is brought into the processing facility and processed to, in some cases, manufacture animal feed. The process converts the byproduct, which consists of waste animal tissue, into stable value-added material like purified animal fats (lard, tallow, and grease) and protein meals (meat, bone meal, and blood meal). Generally, the process is performed by simultaneously drying the animal byproduct and separating the fat from the bone and protein. In some cases, the animal tissue may be blended with other organic material to form feeds. In some cases the animal byproduct includes feathers and hair, and the processing of these materials includes hydrolyzing and drying the material to form feather meal and a hair meal.
In the process of drying the animal byproduct, heat is added to the material resulting in the generation of vapors. These vapors carry odorous compounds such as hydrogen sulfide, ammonia, and volatile organic compounds (VOCs). In most facilities an air scrubbing process is used to reduce or remove some of these odorous vapors prior to their release into the atmosphere. In addition, various vapor streams containing these odorous compounds are condensed separate as many of the condensable vapors from the non-condensable vapors prior to air scrubbing or release to the atmosphere. This greatly reduces the load to the air scrubbing equipment and the environment. It should be appreciated that a rendering facility may generate multiple condensate streams from various process steps. For example, condensate streams may be produced from condensers used in conjunction with a cooker, an evaporator, a disk dryer, a spray dryer, drum dryer, or any other process step in which a vapor stream is produced and can be condensed.
In the process of condensing a vaporous stream, a large portion of the odorous or odor causing compounds are separated prior to air scrubbing thereby forming one or more liquid condensate streams containing these soluble, odor causing compounds. The condensed vapor streams typically are mixed with other waste streams and processed using a waste water pretreatment system, introduced into a biological system for processing, or discharged to a sewer system. In none of these cases, however, are the condensed vapor or condensate streams treated for odor prior to being fed to the waste water pre-treatment system. Therefore, even after mixing with other streams and being further processed prior to discharge, the soluble odor-causing compounds in these condensate streams can be the cause of odor problems in the surrounding atmosphere. In many cases where the condensed vapors from the processing of the animal byproduct material are mixed with other fluid systems and processed in a waste water pretreatment or in a biological treatment system, the odor-causing compounds are liberated through reduced solubility driven by changes in pH, temperature, mechanical aeration, or other means. Accordingly, once liberated, these compounds become an evident source of odor nuisance.
Therefore, there is a need for a method of treating the odor-causing compounds in condensate streams, as such need exists in rendering and pet food processing facilities, as well as other industries that produce vapor streams containing odor compounds that can be condensed, such as oil recovery processes.